The present application relates to semiconductor device fabrication, and more particularly to fabrication of two-sided and bidirectional semiconductor devices.
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
Commonly-owned and co-pending application Ser. No. 14/313,960, which is hereby incorporated by reference, taught novel bidirectional bipolar transistors known as B-TRANs. B-TRANs are three-layer four-terminal bidirectional bipolar transistors having at least two leads on each surface. One junction on each surface of the B-TRAN acts as an emitter or a collector, depending on the polarity of the applied voltage. Conventionally, fabrication of double-sided devices such as B-TRANs and bidirectional IGBTs is complicated and costly, since most conventional fabrication is not designed to allow for multiple electrodes on each wafer surface.
The majority of integrated circuits have all of their individual components fabricated on the front surface of the chip, though electrical contact may be made to the back surface of the chip. The majority of discrete devices having three or more terminals are configured similarly, with the top surface having two or more separate leads, while the entire back surface is another electrical lead. However, restricting one side of a device to only a single electrical lead necessarily precludes the fabrication of any devices having two or more leads on both surfaces.
The present application teaches, among other innovations, methods for fabricating double-sided semiconductor devices, in which multiple leads can be formed on each surface of a device.
The present application also teaches, among other innovations, systems for fabricating double-sided semiconductor devices, in which multiple leads can be formed on each surface of a device.
The present application also teaches, among other innovations, methods for operating systems to fabricate double-sided semiconductor devices, in which multiple leads can be formed on each surface of a device.
The above innovations are implemented, in various disclosed embodiments, by fabrication sequences using at least two handle wafers, comprising a single long dopant diffusion step that can be used to drive-in dopants on both sides of a device. High-temperature-resistant and medium-temperature-resistant handle wafers facilitate fabrication.